[TenTec] 4229 Tuner Balun Replacement?

[Rick - NJ0IP / DJ0IP]

Jerry, we all prefer a link coupler tuner.
Unfortunately there are no commercial units available anymore, at least not
in the amateur radio market.
Most of the old Johnson Viking matchboxes on the market are really grubby
these days, and even if you find a good one, they are very limited in their
matching range.

Sure you "could" build one but unless you are only interested in one or two
bands, the challenge would be finding an appropriate bandswitch.  These are
really quite complex.
I think you would have to build it yourself, which is beyond the ability of
most of us.
Or, as an alternative you could use a Z-match, which requires no bandswitch,
but they have reduced efficiency at some impedances.  There may still be a
high power version of the Z-Match available from UK Linears.

The MFJ and Palstar designs for symmetrical matchboxes are not as good as
the link coupled, but they get the job done in good fashion.  You need some
pennies for those boxes though, but they'll handle a kilowatt.

For 100w, I have found the MFJ-974B to be a great little box.
Previously, at field day, my club used an old Viking 275w version, link
coupled matchbox to match our openwire fed doublet.
It had great difficulties finding a match across all bands.
We had to play with feedline lengths.

The last two years we replaced it with the 974B and were able to obtain a
good match on all bands.
We have retired the Johnson Viking.

Here for high power, I use a home-brew coax balun and a Model 238 tuner.
Works great on ALL bands.  As with any openwire fed antenna, I sometimes
have to "adjust" the feedline length when I change the QTH.

In the February or March edition of QST there was a really great article on
d-i-y 4:1 current baluns.
I suggest building one of these and placing it external to the matchbox,
with a very short length of coax between the balun and the matchbox.  Any of
the solutions proposed in that article will have less loss than any of the
suggestions previously made in this thread (except for the link coupled
matchbox, of course).

73
Rick (running openwire since 1963)


-----Original Message-----
From: tentec-bounces at contesting.com [mailto:tentec-bounces at contesting.com]
On Behalf Of Dr. Gerald N. Johnson
Sent: Saturday, November 13, 2010 6:23 PM
To: tentec at contesting.com
Subject: Re: [TenTec] 4229 Tuner Balun Replacement?



On 11/13/2010 11:21 AM, Jim Brown wrote:
> On 11/12/2010 4:22 PM, Stuart Rohre wrote:
>> Most external baluns are of heavier construction and therefore lower
>> loss potentially, than built in baluns common to 1970's tuner designs.
>
> Loss in ferrite chokes and in baluns wound with ferrites is NOT a
> function of HEAVY construction, but depends primarily on the
> characteristics of the ferrite material (the MIX),  how the chokes are
> wound (mostly the number of turns), and the size of the core.

The LF end of the useful range depends on the raw inductance of the 
winding which comes from the magnetic material and the turns. The first 
stop band going up is when the length of the wire (loaded by dielectric 
of the insulation and the core) gets close to 1/2 wavelength. Going to a 
bigger core adds more wire per turn and tends to lower that HF end. Its 
easiest with a tiny core to get the broadest bandwidth, like the cores 
in a TV splitter that work from 10 to 1000 MHz (and cost $2.98 retail 
assembled).
>
> Likewise, HEATING in the core depends on the loss, the TX power level,
> the balance of the antenna, AND the length of the transmission line into
> which it is inserted.  Using a balun on Field Day (usually 100W) and
> saying it worked fine doesn't mean much. A FAR better test would be
> running 1.5kW through it into difficult lengths of line and with an
> unbalanced antenna (like a Windom) and noting whether or not it got hot.

True. I remember a balun the antenna boys at Collins built and had us 
test with 50 KW from our 250KW VOA transmitter we were developing. The 
first try smashed the core. They had to redesign for better cooling a 
couple times.
>
> Although I own and love a half dozen Ten Tec tuners, I don't use
> twinlead, so I've never given the balun a torture test. :)

I prefer a link coupled tuner with balanced output, the I don't have the 
limitations of the balun on the tuned side.

73, Jerry, K0CQ
>
> 73, Jim K9YC
> _______________________________________________
>
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